This invention relates to a method for detecting defective press punching and a device for performing the method, and more particularly to a method for detecting defective press punching through checking punched condition in a material after the punching is performed and a device for performing the method.
In general, in case of punching a product of a predetermined shape from a plate-shape material by a press, a dimensional interval of punching for each product should be limited to a minimum in order to effectively utilize the material to a maximum.
Now, if the feed speed of the material is changed due to some reasons or the material is smaller than a predetermined dimension, defects tend to occur in the punched product on the ground of superposed punched holes or overrun from the end portion of the material. The resulting defective product when used results in various inconveniences such as inability of fitting with other parts or inability of sealing the joined portions even though the fitting is achieved.
However, it is extremely difficult to accurately judge existence of the foregoing defects by monitoring or checking the shape of the punched product, and particularly, it is almost impossible to detect the minor defect on the end portion of the product to which both punching and bending processes are simultaneously applied.
This invention has been achieved in view of the foregoing actual circumstances, and its object is to provide a method for detecting defective punching of the press, in which defects on the end portion of the product punched by the press can be detected simply and accurately and to provide a device for performing the method.
According to this invention, a material after the product is punched by the press, hereinafter called "blanked material" or simply "blank", is monitored and whether or not the defect exists on the blank is electromagnetically detected, whereby the existence of the defect on the end portion of the product is judged.
Hereinbelow, the method for detecting the defective punching of the press and the device for performing the method according to this invention will be described in details by referring to the embodiments illustrated on the attached drawings.